Plastic-encapsulated power transistors typically comprise a generally thin transistor body with three terminals extending from the body. The transistor body contains an active semiconductor transistor element, and is encapsulated with plastic material. A metal substrate of high thermal conductivity is typically incorporated into the transistor body, and may either be exposed, or encapsulated within the plastic material. The three terminals typically comprise a pair of main current-carrying terminals and a control terminal; for a bipolar transistor, by way of example, the main-current carrying terminals comprise the emitter and collector terminals of the transistor, and the control terminal comprises a base terminal of the transistor. The three terminals typically extend from one end of the plastic-encapsulated transistor body in an orientation generally parallel to a main flat surface of the transistor body. The cross sections of the terminals along their length are typically rectangular, with the ratio of the longer, to the shorter, cross-sectional dimension being about 2 to 1.
Electronic equipment, such as power amplifiers, employ printed-circuit boards on which the majority of electrical connections among different electrical components are made. For assembling efficiency, at least the majority of electrical components are positioned on a top surface of a printed-circuit board (PCB), with respective, conductive "legs" extending substantially all the way through respective apertures in the printed-circuit board. A single, soldering operation is then typically performed using, for instance, the so-called technique of "wave" soldering in which the PCB is placed over a vat of solder in which a wave of solder is created and moved across the lower surface of the PCB. In this procedure, the downwardly protruding conductive legs of the various electrical components on the PCB are simultaneously soldered in place at the lower surface of the PCB. Such simultaneous soldering step is then typically followed by a simultaneous cleaning step, which may employ ultrasonic energy, for simultaneously removing solder from unwanted locations on the lower surface of the PCB.
Where a power transistor is attached to a heat sink, for removing heat from the transistor, the combination of heat sink and transistor is typically quite bulky. This has prevented the "heat-sinked" transistor from being positioned on the PCB with its terminals extending through apertures in the PCB and being soldered to the PCB in the above-described, simultaneous soldering operation. Thus, the prior art has led to a cumbersome procedure in which the PCB is first attached to a chassis, and then the terminals of the heat-sinked transistor are inserted through apertures in the PCB. The transistor terminals are then separately soldered to the PCB, and a separate clean-up step then carried out. While the foregoing soldering and cleanup steps typically assure that the connections made will be capable of carrying high current levels, which may typically reach 20 amps for a power transistor, such steps require a relatively high skill level and a relatively large amount of time to complete.
It would, therefore, be desirable to provide a more efficient method of connecting the terminals of heat-sinked, plastic-encapsulated power transistors to circuits of a printed-circuit board while assuring that the connections so made are capable of carrying high currents.